The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform

Rita M. Linggood - One of the best experts on this subject based on the ideXlab platform.

James W. Langston - One of the best experts on this subject based on the ideXlab platform.

  • Results of a prospective randomized trial comparing standard dose Neuraxis irradiation (3,600 cgy/20) with reduced Neuraxis irradiation (2,340 cgy/13) in patients with low-stage medulloblastoma
    Pediatric neurosurgery, 1996
    Co-Authors: Melvin Deutsch, Patrick R. M. Thomas, James M. Boyett, Patricia A. Aronin, Leland Albright, Jeffrey C. Allen, James W. Langston, Roger J Packer, Jeffrey P. Krischer, Rita M. Linggood
    Abstract:

    Purpose: To determine in a prospective randomized trial the effect on survival, progression-free survival, and patterns of relapse of a decrease in the Neuraxis radiation dose from

  • results of a prospective randomized trial comparing standard dose Neuraxis irradiation 3 600 cgy 20 with reduced Neuraxis irradiation 2 340 cgy 13 in patients with low stage medulloblastoma
    Pediatric Neurosurgery, 1996
    Co-Authors: Melvin Deutsch, Patrick R. M. Thomas, James M. Boyett, Patricia A. Aronin, Leland Albright, Jeffrey C. Allen, James W. Langston, Roger J Packer, Jeffrey P. Krischer, Rita M. Linggood
    Abstract:

    Purpose: To determine in a prospective randomized trial the effect on survival, progression-free survival, and patterns of relapse of a decrease in the Neuraxis radiation dose from

  • Low-grade astrocytoma with Neuraxis dissemination at diagnosis
    Journal of neurosurgery, 1995
    Co-Authors: Amar Gajjar, Richard L. Heideman, James W. Langston, Jesse J. Jenkins, Ravi Bhargava, Robert A. Sanford, Andrew W. Walter, John F. Kuttesch, Michael S. Muhlbauer, Larry E. Kun
    Abstract:

    Little is known about low-grade astrocytoma with Neuraxis dissemination at diagnosis. A review of medical records identified this phenomenon in eight of 150 pediatric patients evaluated between 1985 and 1994 for histologically confirmed low-grade astrocytoma. These patients (five male and three female) ranged in age from 5 months to 20 years (median 8 years). Symptoms of Neuraxis disease were minimal or absent. Primary tumor sites were the hypothalamus in four cases, brainstem/spinal cord in three, and temporal lobe in one. Patterns of dissemination (evaluated by computerized tomography and/or magnetic resonance imaging techniques) appeared to be related to the primary site: hypothalamic tumors metastasized along the ventricular cerebrospinal fluid pathways, and tumors in other locations disseminated along subarachnoid pathways. Following initial treatment with chemotherapy (in three), partial resection (in one), radiation therapy (in three), and chemotherapy plus irradiation (in one), four patients required salvage therapy for progressive or recurrent disease. Seven of the eight patients are alive with stable or progressive disease 6 to 105 months postdiagnosis (median 15 months). Low-grade astrocytoma with initial Neuraxis dissemination is responsive to chemotherapy and radiation, a proportion showing periods of stable disease. The optimum therapy or combination of therapies remains unclear.

  • Neuraxis dissemination in pediatric brain tumors. Response to preirradiation chemotherapy.
    Cancer, 1992
    Co-Authors: Stewart J. Kellie, Edward H. Kovnar, Larry E. Kun, Marc E. Horowitz, Richard L. Heideman, Edwin C. Douglass, James W. Langston, R. Alex Sanford, Jesse J. Jenkins, Diane L. Fairclough
    Abstract:

    Of 29 consecutive children treated for malignant primary tumors of the central nervous system (CNS) at this institution, postoperative examination showed radiographic or cytologic evidence of Neuraxis dissemination in 10 (34%). Given the historically poor results in disseminated CNS tumors treated with surgery and radiation therapy alone, these ten patients were treated prospectively with an investigational Phase II protocol consisting of preirradiation cisplatin (90 mg/m2 on day 1) and etoposide (150 mg/m2 on days 3 and 4). The diagnoses included medulloblastoma (n = 4), malignant glioma (n = 3), cerebral primitive neuroectodermal tumor (n = 1), pineoblastoma (n = 1), and mixed glioma of the brainstem (n = 1). Postoperative Neuraxis scanning with computed tomography, magnetic resonance imaging, or spinal myelography showed measurable intracranial or spinal me-tastases in all children. The cerebrospinal fluid (CSF) cytologic examination was positive for tumor cells in five. The best responses, based on serial imaging of Neuraxis metastases, included two complete responses, four partial responses, and three stable disease states. One patient had progressive disease at the primary site despite stable disease in the spine; progressive Neuraxis disease was documented in only one patient during chemotherapy. Clearance of tumor cells from the CSF was documented in three patients. The adverse effects of chemotherapy, consisting of transient myelosuppression and mild ototoxicity, were minimal. Reversible neurologic deterioration occurred in two patients; one patient became acutely quadriplegic after a prolonged convulsive seizure without radiographic evidence of tumor progression. Cancer 1992; 69:1061–1066.

Thomas M Jessell - One of the best experts on this subject based on the ideXlab platform.

  • sonic hedgehog signaling at gastrula stages specifies ventral telencephalic cells in the chick embryo
    Development, 2000
    Co-Authors: Lena Gunhaga, Thomas M Jessell, Thomas Edlund
    Abstract:

    A secreted signaling factor, Sonic hedgehog (Shh), has a crucial role in the generation of ventral cell types along the entire rostrocaudal axis of the neural tube. At caudal levels of the Neuraxis ...

  • assignment of early caudal identity to neural plate cells by a signal from caudal paraxial mesoderm
    Neuron, 1997
    Co-Authors: Jonas Muhr, Thomas M Jessell, Thomas Edlund
    Abstract:

    The early patterning of the vertebrate central nervous system involves the generation of progenitor cells with distinct fates at rostral and caudal levels of the Neuraxis. We provide evidence that the assignment of early rostrocaudal differences in progenitor cell properties is established by spatial restrictions in the signaling properties of the paraxial mesoderm and epidermal ectoderm. Caudal level paraxial mesoderm secretes a factor, distinct from retinoic acid or fibroblast growth factors (FGFs), that can impose caudal fates on prospective anterior proencephalic progenitors. The caudalizing activity of the paraxial mesoderm can, however, be induced by FGF signaling. The distinct properties of cells at rostral and caudal levels of the neural plate appear to depend, in addition, on the early exclusion of bone morphogenetic proteins (BMPs) from rostral level epidermal ectoderm. Thus, differences in the signaling properties of cell groups that flank the neural plate appear to contribute to the early rostrocaudal identity of neural cells, distinguishing progenitor cells at prospective anterior proencephalic regions from those at more caudal levels of the Neuraxis.

  • Midline cells and the organization of the vertebrate Neuraxis
    Current opinion in genetics & development, 1993
    Co-Authors: Arial Ruiz I Altaba, Thomas M Jessell
    Abstract:

    Vertebrate embryos exhibit a striking midline axis of symmetry that can be recognized in the overall body plan, the framework of skeletal structures and the organization of the nervous system. Cells located at the midline of the embryo during gastrulation have a crucial influence on the establishment of cell identity and pattern within the nervous system. The identification of transcription factors and secreted proteins that are expressed by these midline cell groups has begun to provide a molecular characterization of the organizing centers that establish early neural identity and pattern.

Roger J Packer - One of the best experts on this subject based on the ideXlab platform.

Denise J. Wedel - One of the best experts on this subject based on the ideXlab platform.

  • Anticoagulants, Antiplatelet Therapy, and Neuraxis Blockade
    Anesthesiology Clinics of North America, 1992
    Co-Authors: Terese T. Horlocker, Denise J. Wedel
    Abstract:

    Summary Regional anesthesia can be safely performed in patients receiving anticoagulant or antiplatelet therapy as attested by studies reported by Rao and El-Etr,26 Horlocker et al,11 and Odoom and Sih.21 Therefore, based on the available information, we believe the following recommendations are appropriate: 1. It is generally agreed that in the absence of extraordinary indications, spinal and epidural anesthesia are contraindicated in patients within 24 hours of receiving thrombolytic therapy, having known coagulopathies, or having significant thrombocytopenia. 2. Although the data by Odoom and Sih21 are reassuring, central Neuraxis blockade should probably be avoided in fully anticoagulated patients. However, patients who have received only one or two doses of an oral anticoagulant will not have an increased prothrombin time and may safely undergo regional anesthesia. A prothrombin time may be measured before needle placement if necessary. 3. Patients fully anticoagulated with a continuous heparin infusion should have the infusion discontinued 4 to 6 hours before needle or catheter placement. Subcutaneous low-dose heparin should also not be administered within 4 to 6 hours of a spinal or epidural anesthetic to allow for normalization of the activated partial thromboplastin time. Laboratory verification may be performed before initiation of regional blockade. 4. Epidural or spinal anesthesia followed by systemic heparinization is probably safe, provided adequate precautions are taken.18, 26 Heparinization should not be initiated for at least an hour after needle placement.18, 28 In addition, patients also receiving antiplatelet medications who will undergo subsequent heparinization appear to be at increased risk for spinal hematoma and need to be followed closely. Rao and El-Etra26 recommended careful monitoring of the activated clotting time during heparinization. If needle placement is traumatic or difficult, the decision to proceed with surgery should be reevaluated. Removal of an indwelling epidural catheter in a patient receiving intravenous or subcutaneous heparin should occur 4 to 6 hours after the last heparin dose, and anticoagulation should not be initiated for at least 1 hour after catheter removal. 5. Epidural and spinal anesthesia can be safely performed in a patient receiving antiplatelet therapy.11 Patients with a history of bleeding or bruising may be further evaluated with a preoperative bleeding time. 6. The use of small-gauge needles and the midline approach (thereby avoiding the lateral aspect of the epidural venous plexus) allows more atraumatic needle placement. Epidural catheters should not be inserted more than 3 to 4 cm into the epidural space in order to minimize trauma to the epidural venous structures. 7. Short-acting local anesthetics should be used in patients at increased risk in order to promptly evaluate their neurologic status postoperatively. Likewise, an epidural blockade should be allowed to regress sufficiently before initiating a continuous local anesthetic infusion for postoperative analgesia. A narcotic rather than local anesthetic infusion would allow continuous monitoring of neurologic function and may be a more prudent choice in these patients. It is also worth noting that epidural hematomas have also occurred spontaneously in patients on anticoagulant or antiplatelet medications in the absence of trauma or needle placement.15 The decision to perform spinal or epidural anesthesia on a patient receiving these medications should be made on an individual basis, weighing the risks of hemorrhagic complications and benefits of regional anesthesia for a specific patient. The patient's history should be reviewed to discover any underlying medical conditions with associated bleeding tendencies that would increase the risk. Because it is difficult to predict an individual patient's response to antiplatelet or anticoagulant therapy, laboratory verification may be helpful before initiation of spinal or epidural anesthesia (Table 1). It is most useful clinically to evaluate coagulation parameters that are specific to the clotting defect expected such as the prothrombin time in patients on oral anticoagulants or the activated thromboplastin time in heparinized patients. Although the role of tests such as the thromboelastogram, which measure overall coagulation function, has not been defined at this time, they may prove useful in the future. Needle and catheter placement should be accomplished as atraumatically as possible, and subsequent anticoagulation should be carefully monitored to minimize hemorrhagic complications. The patient should be monitored closely in the perioperative period for early signs of cord compression such as backache or neurologic dysfunction, and any clinical or radiologic evidence of cord compression should be followed by an immediate decompressive laminectomy because recovery is unlikely if surgery is delayed for more than 12 hours.8